Dentifrices are used to clean the teeth, generally with toothpaste and a toothbrush and on a daily basis. The toothpaste will aid in the removal of food particles and tooth discolouration caused by substances such as tobacco, tea or wine in addition to the removal of plaque from the surface of the teeth. Toothpastes will also polish the teeth. Cleaning and polishing the tooth surfaces are affected by (1) mechanical means such as abrasive substances and (2) chemical processes such as materials that dissolve the discolouration.
Over-the-counter teeth whitening preparations have been developed to address the cosmetic preference of many to restore luster to tooth enamel discolored by surface entrapped materials; the term lightening may also be used in conjunction with the advertising and sale of these products. While all dentifrices and mouthwashes contain some cleaning and polishing agents some enamel deposits are not removed completely by these agents under normal use conditions. These preparations may not be formulated with the amount or type of agent required to remove the amount of stains and discoloration which build up due to excessive exposure to the staining agent. For example, smokers often develop discolored enamel because the tars and particulate in exhaled cigarette smoke collect on the teeth. And a number of comestibles can stain or discolor tooth enamel, tea being one example of a beverage where the tannins in the tea quickly deposit on the tooth enamel. Some medicinal agents may cause staining or discoloration via entrapment, though this is not a usual common cause of this type of staining.
Accordingly it has become highly desirable to include within an oral healthcare product materials that will both whiten and gloss the enamel of the tooth surface.
Traditionally, effective whitening and good gloss has been associated with high dentine abrasivity (RDA) values. The RDA of a particular substance or formulation can be readily determined by one skilled in the art. See “A Laboratory Method for Assessment of Dentifrice Abrasivity” John J. Hefferen, Journal of Dental Research, Vol 55, No. 4, 536-573.
The technology of the present invention allows compositions to deliver superior gloss, maximise cleaning and provide effective whitening with a significantly lower RDA value than traditional whitening toothpastes.
Oral healthcare compositions containing water soluble polyphosphate (also known as condensed phosphate) salts such as tripolyphosphate salts, are known for use as chemical agents to clean and whiten the teeth.
WO95/17158 (SmithKline Beecham Corp) discloses and claims a composition for reducing or removing surface deposited stains from natural teeth and dental prostheses comprising a dentally acceptable preparation comprising about 5 to 15% by weight of a water soluble alkali metal tripolyphosphate. Suitably the water soluble alkali metal tripolyphosphate is sodium tripolyphosphate.
WO2005/027858 (Glaxo Group Ltd) relates to dentifrice compositions, in particular compositions comprising a fluoride source and a soluble calcium sequestering agent that is not an oxidising agent, for cleaning natural teeth and dentures. Such compositions show excellent cleaning properties whilst at the same time low abrasion characteristics. These compositions must have an RDA value of below 30 and an IVSR value greater than 50 (when compared to a Control). The calcium sequestering agent, which is present in a proportion of 1-20 wt %, may be a condensed phosphate salt, such as sodium tripolyphosphate. An abrasive material may also be present in a proportion of 0-5 wt % of the composition.
U.S. Pat. No. 6,517,815 (Henkel Kommanditgesellschaft auf Aktien) discloses a dentifrice in the form of an aqueous paste or liquid dispersion, comprising 10% to 30% by weight of a combination of silica polishing agents and aluminium oxide in a ratio by weight of 10:0.2 to 10:2, 20% to 50% by weight of a humectants and 2% to 12% by weight of a condensed phosphate. The condensed phosphates are in the form of an alkali metal or ammonium salt. The aluminium oxide is preferably a lightly calcined alumina with a content of at least 10% by weight of α-aluminium oxide of various γ-aluminium oxides. It is suggested that the special combination of polishing agents (ie the combination of the silica and the alumina) is able to provide a dentifrice having good polishing and cleaning effects with only moderate dentine and enamel abrasion, notwithstanding the presence of the hard alumina polishing component.
U.S. Pat. No. 4,632,826 (Henkel Kommanditgesellschaft auf Aktien) discloses a tooth cream comprising 100 parts by weight of silica polishing agent and 2 to 15 parts by weight of weakly calcined alumina polishing agent. The silica polishing agent consists essentially of silica hydrogel and precipitated silica and the weakly calcined alumina 10 to 50% by weight of gamma aluminium oxide and 50 to 90% by weight of alpha aluminium oxide. The tooth cream is suitable for removing stain, polishing and cleaning the surface of teeth without producing any deep scratches or damage by daily use.
Klüppel et al. J. Soc. Cosmet. Chem., 37, 211-223 (July/August 1986) “Parameters for assessing the cleaning power of toothpastes” compares a number of dentifrice formulations for polishing and scratching effects. Test formulations are described containing as the sole abrasive material either a polishing alumina or a hydrated silica or a mixture of a hydrated silica with a polishing alumina. The results suggest that dentifrice products can be developed with high cleaning power and low dentine abrasion. Whilst the test formulations with increasing amounts of a polishing alumina, as the sole abrasive, can provide good cleaning power this was coupled with an unacceptable increase in enamel abrasion. The best test formulation contained a mixture of a silica abrasive and an alumina abrasive which exhibited a high cleaning value together with an unexpectedly low enamel abrasion value.
It has now been found that dentifrice compositions comprising an aluminium oxide polishing agent and a water soluble condensed phosphate salt (such as an alkali metal tripolyphosphate) in the absence of a silica abrasive material exhibit highly effective cleaning power, excellent gloss and shine whilst at the same time providing low dentine abrasion to the tooth surface. In addition, these dentifrice compositions show superior properties when compared to a corresponding formulation that contains an aluminium oxide polishing agent, a water soluble condensed phosphate salt and a silica abrasive.
Accordingly the present invention provides a dentifrice composition comprising a calcined aluminium oxide polishing agent, a water soluble condensed phosphate and an orally acceptable carrier or excipient; the composition being free of a silica abrasive.
Compositions of the present invention show particularly good polishing, gloss and cleaning of the tooth surface, whilst minimising dentine abrasivity, as shown in the data below. Such compositions also have acceptable enamel abrasivity.
Compositions of the present invention can therefore provide, after brushing, highly polished and smoother tooth surfaces, which may attract less plaque, tartar and/or stain resulting in an overall improvement in oral health.
Aluminium oxide polishes having various degrees of calcination, fineness and powder densities are commercially available. In the present invention a preferred aluminium oxide polish is a low calcined alumina, for example as described in the above noted Henkel patents, suitably comprising from 50% to 90% by weight of α-aluminium oxide and 10% to 50% of γ-aluminium oxide.
Suitable low calcined aluminas are prepared by mild or weak calcination from aluminium hydroxide. Aluminium hydroxide is converted by calcination into α-aluminium oxide (Al2O3), which is thermodynamically stable at temperatures above 1200° C. The thermodynamically unstable Al2O3 forms occurring at temperatures between 400 to 1000° C. are known as γ-forms. The degree of calcination, i.e. the conversion into thermodynamically stable α-aluminium oxide (Al2O3) can be adjusted as required through the choice of temperature and duration of the calcination process. Low calcination gives an alumina with a low α-Al2O3 content and higher γ-Al2O3 compared to high calcination. As the calcinations temperature and time increases, the amount of α-Al2O3 increases and the amount of γ-Al2O3 decreases. These are distinguished from pure α-Al2O3 by a lower hardness of the agglomerate, a larger specific surface and larger pore volumes.
A low calcined aluminia suitable for the present invention is P10 Feinst available from Almatis which is a high polishing alumina having a primary crystal size of <1 micron and an α-Al2O3 content >70%. P10 Feinst is available from Almatis GmbH, Giulinistrasse 2, 67065 Ludwigshafen, Germany. (see also http://www.almatis.com/download/data-sheets/GP-RCP_007_Calcined_Aluminas_for_Polishing_1009.pdf
Suitably the low calcined alumina is present in an amount from 0.1% to 3.0%, for example from 0.2% to 3.0% or 0.5% to 2.0% by weight of the total composition.
A further component of the compositions of this invention is a water soluble condensed phosphate salt, such as an alkali metal pyrophosphate, tripolyphosphate or higher polyphosphate salt, in particular a water soluble alkali metal tripolyphosphate salt. Suitably the sodium form of this salt is preferred, although the potassium or mixed sodium and potassium salts could be used as a preferred embodiment as well. All physical forms can be used, e.g. a hydrate or the dehydrated form.
Most suitably the water soluble alkali metal tripolyphosphate salt is sodium tripolyphosphate.
Suitably the water soluble condensed phosphate salt (such as an alkali metal tripolyphosphate salt) is present in an amount from 1.0% to 20.0%, for example from 2.0% to 15.0% or 5.0% to 10.0% by weight of the total composition.
In addition to the above ingredients, compositions of the present invention may comprise one or more active agents conventionally used in dentifrice compositions, for example, a fluoride source, a desensitising agent, an anti-bacterial agent, an anti-plaque agent, eg. isopropylmethylphenol (IPMP), an anti-calculus agent, an oral malodour agent, an anti-inflammatory agent, an anti-oxidant, an anti-fungal agent, wound healing agent or a mixture of at least two thereof. Such agents may be included at levels to provide the desired therapeutic effect.
Examples of desensitising agents include a tubule blocking agent or a nerve desensitising agent and mixtures thereof, for example as described in WO02/15809 (Block). Examples of desensitising agents include a strontium salt such as strontium chloride, strontium acetate or strontium nitrate or a potassium salt such as potassium citrate, potassium chloride, potassium bicarbonate, potassium gluconate and especially potassium nitrate.
A desensitising agent such as a potassium salt is generally present between 2% to 8% by weight of the total composition, for example 5% by weight of potassium nitrate may be used.
Suitable sources of fluoride ions for use in the compositions of the present invention include an alkali metal fluoride such as sodium fluoride, an alkali metal monofluorophosphate such a sodium monofluorophosphate, stannous fluoride, or an amine fluoride in an amount to provide from 25 to 3500 pm of fluoride ions, preferably from 100 to 1500 ppm. A typical fluoride source is sodium fluoride, for example the composition may contain 0.1 to 0.5% by weight of sodium fluoride, eg 0.204% by weight (equating to 923 ppm of fluoride ions), 0.2542% by weight (equating to 1150 ppm of fluoride ions) or 0.315% by weight (equating to 1426 ppm of fluoride ions).
Such fluoride ions help promote the remineralisation of teeth and can increase the acid resistance of dental hard tissues for combating caries, dental erosion (ie. acid wear) and/or tooth wear.
Compositions of the present invention will contain additional formulating agents such as, surfactants, humectants, non-abrasive (thickening) silicas, flavouring agents, sweetening agents, opacifying or colouring agents, preservatives and water, selected from those conventionally used in the oral hygiene composition art for such purposes.
Suitable surfactants for use in the present invention include anionic surfactants such as a sodium C10-18alkyl sulphate, eg sodium lauryl sulphate. Sodium lauryl sulphate is generally considered to be anionic and strongly charged and is useful if high levels of foaming are desired when brushing teeth.
In addition to anionic surfactants, zwitterionic, amphoteric, cationic and non- or low-ionic surfactants may be used to aid foaming characteristics. When anionic and amphoteric surfactants are used together an optimised foaming system is achieved that will provide both improved mouth feel and good cleaning. Examples of amphoteric surfactants include long chain alkyl (eg. C10-C18 alkyl) betaines, such as the product marketed under the tradename ‘Empigen BB’ by Albright & Wilson and long chain alkyl amidoalkyl betaines such as cocamidopropylbetaine.
A particularly preferred example of an anionic/amphoteric surfactant combination for use in the present invention is sodium lauryl sulphate/cocamidopropylbetaine.
Suitably, the surfactant is present in the range 0.1 to 15%, for example from 0.5 to 10% or from 1.0 to 5% by weight of the total composition
Suitable humectants for use in compositions of the invention include glycerin, xylitol, sorbitol, propylene glycol or polyethylene glycol, or mixtures of at least two thereof; which humectant may be present in the range from 10 to 80%, for example from 20 to 70% or from 30 to 60% by weight of the total composition.
It will be understood that compositions of the present invention may also be used outside the oral cavity, for the cleaning of dentures and the like.
The dentifrices of the present invention are typically formulated in the form of a paste that is suitable for containing in and dispensing from a laminate tube or a pump as conventionally used in the art. Additional examples may include bag-in-can or bag-on-valve delivery systems that utilise a foaming agent such as pentane or iso-pentane.
A typical process for making the composition of this invention involves admixing the ingredients, suitably under a vacuum, until a homogeneous mixture is obtained, and adjusting the pH if necessary.
In order to aid stability, products containing a condensed phosphate should have a high pH value so one or more pH regulators may be added to maintain the pH of the composition at between 7.0-10.0, especially at pH 8.5-9.5. A suitable pH regulator is sodium hydroxide.
The pH is measured when the composition is slurried with water in a 1:3 weight ratio of the composition to water.